diff --git a/tests/conf.py b/tests/conf.py
index 20e9e6b..4bd97e5 100644
--- a/tests/conf.py
+++ b/tests/conf.py
@@ -3,6 +3,8 @@
 ## Make a conf_private.py for personal configuration.
 ## Check conf_private.py.EXAMPLE
 import logging
+from typing import Any
+from typing import Optional
 
 from caldav.davclient import DAVClient
 
@@ -145,7 +147,7 @@
 )
 
 
-def client(idx=None, **kwargs):
+def client(idx: Optional[int] = None, **kwargs: Any) -> DAVClient:
     if idx is None and not kwargs:
         return client(0)
     elif idx is not None and not kwargs and caldav_servers:
@@ -163,8 +165,9 @@ def client(idx=None, **kwargs):
     for kw in kwargs:
         if kw not in CONNKEYS:
             logging.critical(
-                "unknown keyword %s in connection parameters.  All compatibility flags should now be sent as a separate list, see conf_private.py.EXAMPLE.  Ignoring."
-                % kw
+                "unknown keyword %s in connection parameters.  "
+                "All compatibility flags should now be sent as a separate list, see conf_private.py.EXAMPLE.  Ignoring.",
+                kw,
             )
             kwargs.pop(kw)
     return DAVClient(**kwargs)